linux-kernel - Re: [RFC PATCH] xen/x86: Increase xen_e820_map to E820_X

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Date:   Wed, 16 Nov 2016 07:06:31 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Alex Thorlton <athorlton@....com>
Cc:     Jan Beulich <JBeulich@...e.com>,
        David Vrabel <david.vrabel@...rix.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        xen-devel@...ts.xenproject.org, Ingo Molnar <mingo@...hat.com>,
        Russ Anderson <rja@....com>, linux-kernel@...r.kernel.org,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC PATCH] xen/x86: Increase xen_e820_map to E820_X_MAX possible
 entries

On 15/11/16 16:22, Alex Thorlton wrote:
> On Tue, Nov 15, 2016 at 10:55:49AM +0100, Juergen Gross wrote:
>> I'd go with the new error code. What about E2BIG or ENOSPC?
>>
>> I think the hypervisor should fill in the number of entries required
>> in this case.
>>
>> In case nobody objects I can post patches for this purpose (both Xen
>> and Linux).
> 
> This sounds like a good solution to me.  I think it's definitely more
> appropriate than simply bumping up the size of xen_e820_map, especially
> considering the fact that it's theoretically possible for the e820 map
> generated by the hypercall to grow too large, even on a non-EFI machine,
> where my change would have no effect.

Well, it won't help with the current hypervisor, so bumping up the size
of xen_e820_map will still be a good idea. I think using E820_X_MAX is
okay since in the end xen_e820_map will be transferred into a struct
e820map which can't hold more than E820_X_MAX entries (additional
entries are ignored here, so this won't let the boot fail).


Juergen